A couple come to see you following their 18 week ultrasound. They have been told that the ultrasound showed that their baby has spina bifida. The family wish to discuss the situation with a paediatrician.
How common is spina bifida?
The incidence at birth <1 in 200.
The number of cases of spina bifida is declining. This is likely due to earlier ultrasound diagnosis and the increasing use of folic acid supplements by women of child-bearing age.
80% are now diagnosed antenatally and many are terminated in the antenatal period. Blood screening for raised alpha fetoprotein is helpful if positive.
What is spina bifida?
Spina bifida is a congenital lesion of the spinal cord which results in some part of the spinal cord and meninges being exposed.
Spinal lesions are classified into:
- Anencephaly – the natural history is 67% stillborn, 33% neonatal death.
- Encephalocele – the natural history is 23% stillborn, 43% neonatal death. Many of the survivors have a significant disability – spastic quadriplegia, epilepsy, hydrocephalus, and intellectual disability.
- Spina bifida.
..and where is the lesion?
Most spinal defects are in the lower lumbar to sacral region, but they can occur at any level. Most are located posteriorly.
Greater than 97% of cases of spina bifida are associated with Chiari II malformation in the brain. This causes displacement of the cerebellum, fourth ventricle and medulla through the cisterna magna resulting in a banana shaped cerebellum. There is also concavity of the frontal bones resulting in lemon shaped skull and ventriculomegaly.
The more severe lesions can be seen as early as 11-12 weeks, but most are diagnosed at the routine fetal anatomy scan at 18-20 weeks
How can we predict functional outcome?
Ascertainment of the level of the spinal lesion is the most important predictor of functional outcome. MRI may be used to aid in this – but a thorough high resolution US examination is more effective at determining the level of the lesion.
There can be associated deformities of the lower limbs such as club feet and hip dislocation. Most neural tube defects are isolated malformations, but up to 15% have an association with other abnormalities (VSD, renal, IUGR), and 3% have an association with chromosomal abnormalities.
A lipomyelomeningocele is the mildest form of spina bifida – usually there is no Chiari malformation. Mobility issues are harder to predict in these cases though, and they may be progressive. Patients often have incontinence/bowel issues.
The main questions to ask when considering the likely functional outcome are…
- Is this spina bifida?
- Where is the lesion? How big? What type?
- Is there a Chiari malformation?
- Is there hydrocephalus?
- Is there bony deformity?
- Are there leg movements?
- Any other anomalies?
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